Autonomous clocks may drift with time. This drift may not be noticed if clocks are tied and/or synchronized to atomic clocks via, for example, some communication channel. When disconnected for a while, we may notice that our independent clock will diverge from the correct real time. One such example is the clock in our computers. If we disconnect them from a network for a few days, the clock will continue ticking but it will drift seconds away from other computers' clocks that are synchronized to atomic clocks. This drift may present a problem, such as, incorrect creation dates of files, etc.